FIG. 10 is a partial cross-sectional view of a known magnetic sensing element, i.e., spin-valve thin film element, cut from the direction parallel to a surface facing a recording medium.
Referring to FIG. 10, a base layer 1 is composed of Ta, and a seed layer 2 composed of a metal having a body-centered cubic (bcc) structure, for example Cr, is disposed on the base layer 1.
A multilayer film T1 is deposited on the seed layer 2. In the multilayer film T1, a free magnetic layer 3, a nonmagnetic layer 4, a pinned magnetic layer 5, an antiferromagnetic layer 6, and a protective layer 7 are disposed in that order.
The free magnetic layer 3 is composed of a Heusler alloy such as Co2MoAl, the nonmagnetic layer 4 is composed of Cu, the pinned magnetic layer 5 is composed of CoFe, the antiferromagnetic layer 6 is composed of PtMn, and the protective layer 7 is composed of Ta.
An exchange coupling magnetic field is generated at the interface between the antiferromagnetic layer 6 and the pinned magnetic layer 5, thereby pinning the magnetization of the pinned magnetic layer 5 in the height direction (in the Y direction in the figure).
Hard bias layers 8 composed of a hard magnetic material such as CoPt are disposed at each end of the free magnetic layer 3. The upper parts, the lower parts, and the ends of the hard bias layers 8 are insulated by an insulating layer 9. The magnetization of the free magnetic layer 3 is aligned in the track width direction (in the X direction in the figure) by a longitudinal bias magnetic field from the hard bias layers 8.
When an external magnetic field is applied to the magnetic sensing element shown in FIG. 10, the magnetization direction of the free magnetic layer 3 is relatively changed to that of the pinned magnetic layer 5. Consequently, the resistance of the multilayer film T1 is changed. Under a constant sense current, such a change in resistance is detected as the change in current or voltage of the sense current, thus detecting the external magnetic field.
The Heusler alloy, which is the material of the free magnetic layer, shows ferromagnetism depending on the composition. The term “Heusler alloy” is a generic term of metallic compounds having a Heusler crystal structure.
Japanese Unexamined Patent Application Publication No. 8-250366 discloses a magnetic sensing element including a thin film composed of a Heusler alloy. The thin film is disposed on a metal underlayer having the body-centered cubic (bcc) structure.
According to the above patent document, the thin film composed of a Heusler alloy is disposed on the metal underlayer having a bcc structure, and consequently, the thin film can be formed as an adequately crystallized film.
However, the above patent document specifically describes neither crystal orientations of the underlayer and the Heusler alloy film nor crystallographic matching relationship between the underlayer and the Heusler alloy film.
In addition to the crystal structure of the underlayer, which is disposed under Heusler alloy film, for example, the crystal orientation of the underlayer and the crystallographic matching between the Heusler alloy and the underlayer must be considered so that the Heusler alloy is formed as an adequately crystallized film.
The description in the above patent document does not provide specific conditions for producing a thin film composed of an adequately crystallized Heusler alloy. In reality, it may not be possible to produce such a thin film.